This invention relates to a microwave alcohol fuel sensor, and more particularly to a microwave alcohol fuel sensor for automobile internal combustion engines.
Recently, alcohol fuel has come into notice as fuel for automobile internal combustion engines in place of gasoline fuel. The alcohol fuel is advantageous in that the fuel can be used for present automobiles without changing greatly the constructions and that an amount of atmosphere pollution substances into which the fuel is converted by the combustion of the fuel are less than the gasoline fuel.
One of the alcohol fuels is a mixture of alcohol and gasoline. When such a mixture is used, it is important to detect precisely the mixing ratio and to run the engine under the most appropriate condition. In order to satisfy the above, it is necessary to develop a practical method of simply and precisely measuring the mixing ratio or the alcohol content.
Various methods of measuring the mixing ratio are proposed. When the methods are really used in automobiles, however, they should meet various requirements of the automobiles. At present, therefore, an electrostatic capacity method of the various methods is most likely to put into practice. According to the electrostatic capacity method, the mixing ratio is measured by detecting output voltage established between a pair of parallel electrodes disposed in the fuel. However, the change in the output voltage level according to alcohol content rate is very small, for example 1.7 volt at the maximum. Further, the output voltage changes much greater at relatively small alcohol content rate than at large content rate. Therefore, it seems that improvements should be put into this method to effect a precise measurement.